Interface History on Strain Field Evolution in Epoxy Resins
Edward Garboczi, Newell Moser, Jena McCollum, Jared Strutton, Abby Jennings, Brandon Runnels
To determine the viability of digital image correlation in the analysis of additively manufactured thermosets, we devised a testing method to examine the effect of interface history (i.e., time between interface formation and original material deposition) on localized mechanical properties. Interfaces were formed in diglycidyl ether of bisphenol A (DGEBA)/diethylenetriamine (DETA) epoxy resins with various DETA concentrations. Time to gel point and full cure was assessed by rheology and Fourier transform infrared spectroscopy (FTIR) for each composition. From here, dogbone samples were fabricated with an interface formed at either the gel point or at full cure for each composition. Key findings show that tensile strength and modulus deteriorate with the presence of an interface regardless of history or initiator (DETA) concentration. However, samples with an interface demonstrate high strain regions near the interface prior to fracture. Micro x-ray computed tomography revealed high density regions at the interface that increased with both cure time and initiator concentration. Fourier transform infrared spectroscopy showed that the interface demonstrated higher cure completion than the sample interior, resulting in a stiffer epoxy at the interface versus the interior. These findings were confirmed by atomic force microscopy modulus mapping at the interface. Finally, computational modeling of epoxy in uniaxial tension with an increasing number of stiff inclusions demonstrated that inclusion content correlated to increased, localized stress concentrations. These findings will aid in the understanding of fracture phenomenon in additively manufactured thermosets and point to digital image correlation as a useful tool in epoxy interface detection.
, Moser, N.
, McCollum, J.
, Strutton, J.
, Jennings, A.
and Runnels, B.
Interface History on Strain Field Evolution in Epoxy Resins, ACS Applied Polymer Materials, [online], https://doi.org/10.1021/acsapm.1c01930, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=933358
(Accessed December 8, 2023)